Diagram of refraction

When viewing at a certain angle, the straw appears to bend, due to refraction of light as it moves into the air

A ray of light being refracted in a plastic block.

Refraction is the change in direction of a wave, caused by the change in the wave's speed. Examples of waves include sound waves and light waves. Refraction is seen most often when a wave passes from one transparent medium to another transparent medium. Different types of medium include air and water.